This invention relates to a non-aqueous fluid polymer suspension for use as a rheology modifier and fluid loss reducer in oil field applications. More particularly, this invention is directed to the use of an environmentally acceptable fluidized polymer suspension of cellulosic ethers and guar and its derivatives for use in oil field applications such as completion fluids, drilling fluids, fracturing fluids, stimulation fluids and oil well cement slurries.
Prior to the present invention, offshore drilling operations have caused much pollution of our oceans and waterways to the point that many countries, especially the Scandinavian countries, have started to impose environmental restrictions for operations in these oceans and waterways. The pollution has severely endangered the fish and plant life in these bodies of water and threatens the balance of the ecology systems of these waters. In the past few years, severe environmental restrictions in the oil well drilling activities, especially in North Sea sector, have been made in the direction of requiring more environmentally friendly drilling fluid systems. In this category, water based fluid systems are most preferred assuming all chemicals contained in the fluid systems exhibit low toxicity and high biodegradability. The chemicals used in these fluid systems are regarded as separate components that should meet the environmental regulations for nonpolluting drilling fluids.
Drilling fluids can be classified on the basis of their principle component, which is water, oil, pseudo-oil, or gas. Within each broad classification are divisions based on composition or chemistry of the fluid or the dispersed phase. Frequently, twoxe2x80x94and sometimes all fourxe2x80x94of these fluids are present in a drilling operation at the same time. Water-based drilling fluids make up about 90% of all drilling fluids and can be environmentally friendly.
Water-based drilling fluids have water as a continuous phase and are regarded as environmental friendly. The make up water may contain several dissolved substances, generally including alkalies, salts, organic polymers and various insoluble mineral substances in suspension. Depending upon the quality of the make up water, composition and the desired properties of the drilling fluid, organic polymers may be selected from polyanionic cellulose (PAC) and carboxymethylcellulose (CMC) to thicken and control the fluid loss of water-based drilling fluids. They are the most widely used cellulose ethers in drilling fluids. For technical and economical reasons, they are often used in combination with xanthan gum and starch or its derivatives.
Oil-based drilling fluids have diesel and occasionally crude oil as a continuous phase with both internal water and solid phases. Fluids with less than 5-10 volume % of water are called oil-based muds whereas those with higher water contents are called invert oil-emulsion muds, or simply inverts. These oil-based drilling fluids cause the most pollution because of the nature of their components being nonbiodegradable and toxic and containing aromatic hydrocarbons.
However, in the North Sea sector, the potential for continued use of oil based drilling fluids is restricted because of the new regulatory requirements regarding the discharge of such drilling fluids as well as the contaminated drilled cuttings.
Until 1992, two separate conventions (Oslo, Norway in 1974 and Paris, France in 1978) were established to regulate and protect Marine environment. They were administered respectively by Oslo and Paris commissions. Initially, the Oslo commission""s task was to xe2x80x9cRegulate and Control the Dumping at Sea of Industrial Wastes, Sewage Sludge and Dredged Material and the Incineration at Sea of Liquid Industrial Wastesxe2x80x9d. The dumping of industrial wastes and sewage sludge and incineration at sea have now been phased out. Next to Oslo convention, it was felt necessary at this time to draw up a similar document, dealing not with the prevention of marine pollution by dumping, but instead with the prevention of marine pollution by discharges of dangerous substances from land-based sources, water sources or pipelines. Negotiations on this topic resulted in the completion of the Paris convention for xe2x80x9cthe prevention of Marine Pollution from Land-Based Sourcesxe2x80x9d. The Paris commission was involved in a thorough review of the use and manufacture of various substances in order to establish the best environmental practice or best available techniques to prevent pollution.
In 1992, a new Convention for the Protection of the Marine Environment of the North-East Atlantic (the xe2x80x9cOSPARxe2x80x9d Convention) was adopted together with a final action plan to guide the future work of the commissions. The OSPAR convention did enter into force in early 1998. The OSPAR commission has the status of an international organization in the terms of British legislation. In 1995 the OSPAR commission introduced the Harmonized Offshore Chemical Notification Format (xe2x80x9cHOCNFxe2x80x9d) to create a mandatory control system for the use and discharge of offshore chemicals. Suppliers of chemicals that are used offshore were now obligated to perform several ecotoxicity tests so that the effect of the chemicals could be assessed. Chemicals are classified into 6 different hazardous group categories (A-E, Z) with group xe2x80x9cExe2x80x9d being the least hazardous (like CMC, HEC, Guar). Group xe2x80x9cAxe2x80x9d being the most hazardous chemical that should be only used when it can be demonstrated that such usage presents an acceptable risk to the marine environment. Group xe2x80x9cZxe2x80x9d chemicals (such as standard commercially available mineral oils used for oil based muds (OBMs)) must only be used in xe2x80x9cZeroxe2x80x9d discharge applications.
In offshore drilling wells, the carrying capacity of the drilling fluid must be high enough to remove drilling cuttings and other formation material that may fall into the well bore and low enough to prevent overloading site pumping equipment that may result in risk of fracturing the formation. These drilled solids are carried up through the annulus to the surface where they are separated and disposed. In addition, for maximum drilling rate, a low effective viscosity is desired at shear rates generated through the bit nozzles in the range of 10,000-100,000 secxe2x88x921. Drilling fluids are normally shear thinning, with apparent viscosity decreasing with increasing shear rate.
Hydrophilic polymers are commonly used in oil field servicing applications which most of them are brought to the site as dry particulate solids. If such hydrophilic polymers were mixed directly with other servicing ingredients and water, in certain instances these ingredients would tend to agglomerate and would be difficult to use. In order to obviate such problem, fluid polymer suspensions were developed and are currently being used to deliver the hydrophilic polymers to the work sites.
Examples of such fluid polymer suspensions for use in oil field servicing applications that are oil-based are U.S. Pat. Nos. 5,001,231, 5,151,131, and 4,566,977. These patents disclose fluid polymer suspension compositions that include diesel, mineral or paraffin oil, a surfactant, water, organophilic clay, and a cellulose ether or guar for oil field servicing applications.
The most used solvents cited in the prior art include mineral oil, kerosene, diesel fuel, glycols and tall oil fatty acid (TOFA). With the exception of glycol and TOFA, the hydrocarbon-based solvents that are commercially available and are also used in oil-based drilling fluids are no longer acceptable for certain areas. Although these systems in the past solved the mixing and mobility problem of the hydrophilic polymers, they do not meet the new environmental regulations, particularly in the North Sea sector. Hence, there still is a need for environmentally acceptable fluid polymer suspensions to meet the new environmental standard requirements.
The present invention is directed to a water free oil based fluid polymer suspension composition for use as a rheology modifier and fluid loss reducer in oil or gas well servicing fluids comprising a hydrophilic polymer, an organophilic clay, a stabilizer and a white medicinal oil that has a low viscosity, has no aromatic content, has a high flash point, has a low pour point, is food contact approved, is non-toxic, and is biodegradable, whereby this FPS composition is environmentally acceptable for use in onshore and offshore oil field servicing fluids and is awarded a classification in category group xe2x80x9cDxe2x80x9d by Center for Environment, Fisheres and Aquaculture Science (CEFAS) under the revised Offshore Chemical Notification Scheme (OCNS) for use in North-Sea.